As a rule, a processing apparatus for photographic sheet material comprises several vessels each of which contains a treatment liquid, such as a developer, a fixer and a rinse liquid. As used herein, the term sheet material includes not only photographic material in the form of cut sheets, but also in the form of a web unwound from a roll. The sheet material to be processed is transported through these vessels in turn, by transport means such as one or more pairs of drive rollers, and thereafter optionally to a drying unit. The time spent by the sheet material in each vessel is determined by the transport speed and the dimensions of the vessel in the sheet feed path direction.
A typical apparatus comprises a developing station followed by second and third treatment stations, which may, for example, be a fixing station and a washing station. The apparatus may have a generally horizontal or vertical configuration.
From time to time it is necessary to clean the processing apparatus, in order to remove debris which may derive from the sheet material itself and deposits derived from the treatment liquids. The usual process for cleaning a processing apparatus, whether of the vertical or horizontal configuration, is to drain the treatment liquids and to flush the apparatus through with cleaning liquid. Water, optionally containing various additives and optionally at an elevated temperature, is the usual cleaning liquid.
For environmental reasons, there is a desire to reduce the use of all raw materials used in a processing machine, including water and this is particularly the case where the apparatus is being used in an area where there is a shortage of water.
European patent application EP-A-0 774 691 (Agfa-Gevaert NV) discloses a method of cleaning a photographic sheet material processing apparatus having a vertical configuration in which cleaning liquid passes by gravity from one cell to another.
Such a method is limited in its applicability to vertical apparatus and in any event is not optimally efficient in terms of total liquid usage.